Mass spectrometer ion source with dual interlocked valve means for evacuation purposes



Sept. 23, 1969 YOSHIO WADA ETI'AL 3,469,093

MASS SPECTROMETER ION SOURCE WITH DUAL INTERLOCKED VALVE MEANS FOR EVACUATION PURPOSES Filed March 27. 1967 Y sH WADA En'I WATANABE Ta kA SWLUKI I N VENTOR$ BY wo wkflw a; ia-w M US. Cl. 250-413 2 (Ilaims ABSTRACT OF THE DISCLOSURE An ion source for a mass spectrometer having an analyzation region connected to the ion source housing by a main channel, within which is a first valve means. The main channel has an aperture slit located at the end of the housing, and the region of the main channel between the aperture slit and the first valve means is connected to the housing by a. second channel that has a second valve means for closing said channel when the main channel is open.

Generally, an ion source for mass spectrometers includes a housing that is connected to a vacuum pump utilized to maintain a vacuum within the housing. Within the housing are two electrodes for ionizing a specimen of a material to be analyzed. The specimen is placed between the electrodes and subjected to a high frequency spark discharge created by the electrodes to produce an ion of the specimen. The ion thus produced is accelerated out of the housing to an analyzer region of the mass spectrometer which is generally an arcuated region in which the ion is magnetically deflected, the angle of deflection giving rise to the basis of analysis.

In currently utilized mass spectrometers, the only connection between the ion source and the analyzer region is channel that houses an airlock valve or a ball valve with plunger. These valve means isolate the ion source from the analyzer region when it is desired to exchange specimens. The end of the channel that is connected to the ion source is capped with a main slit which controls the accelerated ion beam and prevents high pressure gas formed in the ion source from passing unnecessarily into the analyzer region of the spectrometer.

When it is necessary to change the specimen, the valve means must be closed in order to isolate the ion source from the analyzer region. The valve means must be closed prior to the specimen change, since changing the specimen requires that the ion source be opened to the atmosphere. In this case, the channel region between the main slit and the valve means is also exposed to the atmosphere, thereby substantially reducing any vacuum in thi region. Once the new specimen has been secured in the ion source and the ion source housing closed, re-evacuation of the housing can be effected quite rapidly up to the required vacuum. However, this is not the case with the channel region defined by the main slit and the valve because the aperture slit is extremely narrow which results in a pressure differential between the ion source and said channel region.

The present invention provides an ion source for the mass spectrometer which has a second channel connected between the ion source housing and the main channel, whereby the region defined by the main slit and the valve to be evacuated more rapidly and whereby undesirable pressures applied to the main slit caused by the pressure difierential arising between an ion source and a region that is defined by the slit and the valve when evacuating the ion source and/or breaking the ion source vacuum are avoided.

nited States Patent 3,469,093 Patented Sept. 23, 1969 In the accompanying drawing we have shown one preferred embodiment of our invention in which the single figure shows a sectional view along an axial plane of an ion source embodying the invention.

An ion source housing 1, preferably of cylindrical configuration, is provided with an end wall 2 secured to the housing so as to be vacuum tight and an ion source 3. Main channel 4, that connects the ion source with an analyzer region 5, has a region 29 of larger diameter than the remainder of the channel for conveniently installing main slit 6. Slit 6 is located over aperture 7 at the end of the channel facing the ion source and has a very small aperture slit 8 in the center thereof so as to permit passage of ions therethrough.

A second channel 10 extends from ion source housing 1 to a valve seat 9 machined on the narrow section of the main channel. Leaf spring 12, which serves to close the second channel, is secured within the second passage by means of screw 13. A duct extends from the narrower portion of main channel 4 to the exterior of the member containing the channel at an angle to the axis of the channel, and plunger 15 is arranged to move within this duct. At the inner end of the plunger are fixed confronting portions 16 and 17 held in spaced relation to each other. A steel ball 18 having an annular groove 19 on its undersurface is mounted in sliding engagement with portion 16. A collar 20 secured to the under surface of the steel ball is arranged between the confronting portions 16 and 17 in such a manner as to be in sliding contact with them. Plunger 15 extends in a cylinder 14 and is secured in threaded engagement in tapped hole 21 of a sealing block 22 which is connected to the outer wall of cylinder 14. Screw 23 secures sealing block 22 to the outer wall of cylinder 14. Flexible bellow 25 seals the plunger within the cylinder. Handle 24 is provided for moving the plunger by moving screw threads 26. In this way channel 4 is opened or closed by means of the steel ball engaging and disengaging with valve seating 9. Shaft 27 is mounted on the steel ball and is held in coaxial position with respect to the axis of plunger 15 to force the leaf spring up when the ball is engaged with its seating.

When specimen exchange is carried out, the plunger is forced inward by turning handle 24 to close main channel 4 by engaging steel ball 18 with valve seat 9. As shown in the drawing, the shaft 27 pushes the leaf spring 12 up and interior 28 of the ion source housing is in communication with region 29 between the slit and the ball valve which comprises ball 18 and seating 9. The ion source housing 1 is then opened and the first specimen is replaced with a second specimen. This permits air to enter interior 28 and region 29 simultaneously. After the specimen exchange has been carried out in the ion source, the housing is again closed and the interior is evacuated by means of a vacuum source 30. When the degree of vacuum in region 29 and interior 28 becomes sufficiently high, the steel ball is disengaged and shaft 27, opening second channel 10, is withdrawn until main chanel 4 is completely opened. The ion source is now united with the analyzer region while the second channel is shut off by means of the leaf spring without exercising any adverse effect on the slit. High voltage is then fed to electrodes 31 and 32 from an appropriate high voltage source (not shown) and an ionizing electron beam is emitted therefrom. Analysis is made in the conventional manner in the analyzation region of the mass spectrometer, which has been appropriately evacuated by vacuum pump 11.

As mentioned above, according to the invention, the mass spectrometer is so constructed that when the ion source and the analyzer region are disconnected by closing the main channel with the ball valve, the second channel is opened by means of the shaft so as to unite the ion source and the region between the slit and the ball valve, and when the ion source is united with the analyzer region by withdrawing the steel ball from the seating, the leaf spring disconnects the second channel. Evacuation of the ion source, and the region defined by the slit and the ball valve can be accomplished quite speedily by means of the second channel without adversely afiecting the slit in the end wall of the ion source.

While we have shown and described one preferred embodiment of our invention, it may be otherwise embodied within the scope of the appended claims.

We claim:

1. An ion source in mass spectrometers having an ion source housing, an analyzation chamber, means forming a main channel connecting said housing and said chamber, an aperture slit located at the housing end of said main channel, and means for evacuating the mass spectrometer, the improvement comprising in combination therewith:

(a) a valve seat in the main channel;

(b) a first valve means;

4 i a (c) a second channel connecting said housing with the region of said main channel between said aperture slit and said valve seat for rapid evacuation of said region of said main channel when said first valve means is closed; and (d) a second valve means located in said second channel for closing said second channel when said first valve means is disengaged from said valve seat to open said main channel,

2. The improvement set forth in claim 1 including means on said first valve means for operating said second valve means.

References Cited UNITED STATES PATENTS 2,570,124 10/1951 Hernqvist 2504l.9 3,187,179 8/1962 Craig et al 2504l.9

RALPH G. NILSON, Primary Examiner S. C. SHEAR, Assistant Examiner 

